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Mineral Resources > Online Spatial Data > Geology > by state > Wisconsin Geology

Geologic units in Iron county, Wisconsin

[Additional scientific data in this geographic area]

Gabbroic rocks of Keweenawan affinity (Middle Proterozoic) at surface, covers 3 % of this area

Gabbroic rocks of Keweenawan affinity - gabbro, anorthosite, granite, peridotite

Lithology: gabbro; anorthosite; granite; peridotite

Oronto Group; Freda Sandstone (Middle Proterozoic) at surface, covers 4 % of this area

Oronto Group; Freda Sandstone - Mainly reddish-brown, medium- to fine-grained lithic arkosic sandstone, siltstone, and micaceous silty shale.

Lithology: arkose; siltstone; shale

Granophyre (Middle Proterozoic) at surface, covers 0.2 % of this area

Granophyre

Lithology: granite

Powder Mill Group; Kallander Creek Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Powder Mill Group; Kallander Creek Volcanics - Basalt, andesite and lesser rhyolite flows. Basalt flows near base of the formation contain plagioclase phenocrysts, some in radiating clusters

Lithology: basalt; andesite; rhyolite

Oronto Group; Freda Sandstone (Middle Proterozoic) at surface, covers < 0.1 % of this area

Oronto Group; Freda Sandstone - Mainly reddish-brown, medium- to fine-grained lithic arkosic sandstone, siltstone, and micaceous silty shale.

Lithology: arkose; siltstone; shale

Puritan Quartz Monzonite (Late Archean) (Late Archean) at surface, covers < 0.1 % of this area

Puritan Quartz Monzonite (Late Archean) - Pink to pinkish-gray, medium- to coarse-grained, equigranular to inequigranular granite to granodiorite in Puritan batholith south of Gogebic Range. Age 2710 +/- 140 Ma (Sims and others, 1977)

Lithology: granite; granodiorite

Menominee Group; Blair Creek Formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee Group; Blair Creek Formation - Dominantly dark-gray, massive, porphyritic tholeiitic basalt. Includes a basal conglomerate and a lean iron-formation in middle of formation

Lithology: basalt; iron formation; conglomerate

Mafic metavolcanic rocks (Early Proterozoic) at surface, covers 0.3 % of this area

Mafic metavolcanic rocks - Dominantly tholeiitic basalt and basaltic andesite flows and tuffs; associated with sheet dikes, massive and layered metagabbro, and ultramafic rocks. In northeastern Wisconsin, rocks have been named the Quinnesec Formation.

Lithology: basalt; andesite; gabbro; ultramafic intrusive rock

Baraga Group; Michigamme Formation, undivided (Early Proterozoic) at surface, covers 0.3 % of this area

Baraga Group; Michigamme Formation, undivided - Thick and stratigraphically varied formation of sedimentary and less abundant volcanic rocks. Metamorphosed graywacke is predominant rock of Michigamme Formation. Calcareous concretions common. Metamorphosed from cholorite to sillimanite grade (Cannon, 1986). Mapped undivided in poorly exposed areas

Lithology: graywacke

Baraga Group; Tyler Formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Baraga Group; Tyler Formation - Light- to dark-gray, feldspathic, fine-grained sandstone, argillaceous siltstone, and argillite. Near base, ferruginous argillite contains beds of cherty sideritic and pyritic iron-formation

Lithology: sandstone; siltstone; iron formation; argillite

Copper Harbor Conglomerate (Middle Proterozoic) at surface, covers 0.3 % of this area

Copper Harbor Conglomerate - Red lithic conglomerate and sandstone; mafic to felsic volcanic flows similar to those of the unnamed formation (unit Yu) are interlayered with the sedimentary rocks.

Lithology: conglomerate; sandstone; basalt

Portage Lake Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Portage Lake Volcanics - Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.

Lithology: basalt; andesite; rhyolite; mudstone

Metabasalt (Late Archean) (Late Archean) at surface, covers 11 % of this area

Metabasalt (Late Archean) - Derived from mafic to intermediate pyroclastic rocks and massive to pillowed lava flows. Unit mapped as Ramsey Formation by Prinz (1981) south of Gogebic Range; mapped as Mona Schist and Kitchi Schist in northern complex of Marquette District.

Lithology: meta-basalt; tuff; schist

Migmatitic gneiss and amphibolite (Late to Early Archean) (Archean) at surface, covers 6 % of this area

Migmatitic gneiss and amphibolite (Late to Early Archean) - Varied gneisses of mostly unknown age in cores of gneiss domes and fault-bounded uplifts (Archean gneiss terranes). Except for the Watersmeet dome (Late to Early Archean), all dated rocks are Late Archean. Includes granite of Late Archean age that transgresses gneisses and amphibolite.

Lithology: gneiss; amphibolite; granite

Portage Lake Volcanics (Middle Proterozoic) at surface, covers 3 % of this area

Portage Lake Volcanics - Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.

Lithology: basalt; andesite; rhyolite; mudstone

Biotite schist (Early Proterozoic) at surface, covers 17 % of this area

Biotite schist - Metamorphosed graywacke in poorly exposed areas in northwestern Wisconsin. Sample at one locality (near Blockhouse Lake, 10 km northeast of Park Falls, T. 40 N., R. 1 E.) has a U-Pb zircon age of 1852 +/- 6 Ma (Sims and others, 1985b)

Lithology: schist

Menominee Group; Ironwood Iron-formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Menominee Group; Ironwood Iron-formation - Interbedded cherty and slaty iron-formation. Locally, secondary enrichment has formed "soft ore" bodies. In eastern part of Gogebic Range, Ironwood Iron-formation is intercalated with pyroclastic rocks of Emperor Volcanic Complex, and in eastern half of T. 47 N., R. 43 W. (where mapped within unit Xip) consists entirely of black slate

Lithology: iron formation; slate

Puritan Quartz Monzonite (Late Archean) (Late Archean) at surface, covers 15 % of this area

Puritan Quartz Monzonite (Late Archean) - Pink to pinkish-gray, medium- to coarse-grained, equigranular to inequigranular granite to granodiorite in Puritan batholith south of Gogebic Range. Age 2710 +/- 140 Ma (Sims and others, 1977)

Lithology: granite; granodiorite

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member (Middle Proterozoic) at surface, covers < 0.1 % of this area

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member

Lithology: rhyolite

Menominee Group; Blair Creek Formation (Early Proterozoic) at surface, covers 11 % of this area

Menominee Group; Blair Creek Formation - Dominantly dark-gray, massive, porphyritic tholeiitic basalt. Includes a basal conglomerate and a lean iron-formation in middle of formation

Lithology: basalt; iron formation; conglomerate

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member (Middle Proterozoic) at surface, covers 0.9 % of this area

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member

Lithology: rhyolite

Oronto Group; Freda Sandstone; Conglomerate member (Middle Proterozoic) at surface, covers 0.5 % of this area

Oronto Group; Freda Sandstone; Conglomerate member

Lithology: conglomerate

Jacobsville Sandstone (Middle Proterozoic) at surface, covers 0.2 % of this area

Jacobsville Sandstone - Red, brown, and white quartzose sandstone, and minor siltstone, shale and conglomerate

Lithology: sandstone; siltstone; shale; conglomerate

Jacobsville Sandstone (Middle Proterozoic) at surface, covers < 0.1 % of this area

Jacobsville Sandstone - Red, brown, and white quartzose sandstone, and minor siltstone, shale and conglomerate

Lithology: sandstone; siltstone; conglomerate; shale

Powder Mill Group; Kallander Creek Volcanics (Middle Proterozoic) at surface, covers 5 % of this area

Powder Mill Group; Kallander Creek Volcanics- Basalt, andesite and lesser rhyolite flows. Basalt flows near base of the formation contain plagioclase phenocrysts, some in radiating clusters

Lithology: basalt; andesite; rhyolite

Metabasalt (Late Archean) (Late Archean) at surface, covers < 0.1 % of this area

Metabasalt (Late Archean) - Derived from mafic to intermediate pyroclastic rocks and massive to pillowed lava flows. Unit mapped as Ramsey Formation by Prinz (1981) south of Gogebic Range; mapped as Mona Schist and Kitchi Schist in northern complex of Marquette District.

Lithology: meta-basalt; tuff; schist

Porcupine Volcanics (Middle Proterozoic) at surface, covers 0.3 % of this area

Porcupine Volcanics - Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks

Lithology: rhyolite; basalt; andesite; mixed clastic/volcanic

Baraga Group; Tyler Formation (Early Proterozoic) at surface, covers 5 % of this area

Baraga Group; Tyler Formation - Light- to dark-gray, feldspathic, fine-grained sandstone, argillaceous siltstone, and argillite. Near base, ferruginous argillite contains beds of cherty sideritic and pyritic iron-formation

Lithology: sandstone; argillite; iron formation

Powder Mill Group; Siemens Creek Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Powder Mill Group; Siemens Creek Volcanics - Dark-gray basalt and minor porphyritic andesite. Generally strongly magnetic with reversed remanent magnetism. Underlain by a thin unit of quartzose sandstone (Bessemer Quartzite).

Lithology: basalt; andesite

Menominee Group; unexposed magnetic unit (Early Proterozoic) at surface, covers 0.2 % of this area

Menominee Group; unexposed magnetic unit - Surrounds gneiss domes in Gogebic County, Mich. and Vilas County, Wisc., and occurs in north-central Dickinson County. Probably correlative with part of Blair Creek Formation (unit Xbc). Previously correlated with uppermost unit of Blair Creek Formation (Sims and others, 1984).

Lithology: iron formation; slate

Copper Harbor Conglomerate (Middle Proterozoic) at surface, covers < 0.1 % of this area

Copper Harbor Conglomerate - Red lithic conglomerate and sandstone; mafic to felsic volcanic flows similar to those of the unnamed formation (unit Yu) are interlayered with the sedimentary rocks.

Lithology: conglomerate; sandstone; lava flow

Powder Mill Group; Siemens Creek Volcanics (Middle Proterozoic) at surface, covers 2 % of this area

Powder Mill Group; Siemens Creek Volcanics- Dark-gray basalt and minor porphyritic andesite. Generally strongly magnetic with reversed remanent magnetism. Underlain by a thin unit of quartzose sandstone (Bessemer Quartzite).

Lithology: basalt; andesite

Oronto Group; Freda Sandstone; Conglomerate member (Middle Proterozoic) at surface, covers < 0.1 % of this area

Oronto Group; Freda Sandstone; Conglomerate member

Lithology: conglomerate

Gneiss and amphibolite (Late Archean, 2.640-2.750 Ma) (Late Archean) at surface, covers 14 % of this area

Gneiss and amphibolite (Late Archean, 2.640-2.750 Ma) - Interlayered quartzofeldspathic gneiss and amphibolite in Marenisco, Mich., area and northwestern Wisconsin. Protoliths are bimodal intermediate and mafic volcanic rocks (Sims and others, 1984).

Lithology: gneiss; amphibolite

Oronto Group; Nonesuch Shale (Middle Proterozoic) at surface, covers 0.2 % of this area

Oronto Group; Nonesuch Shale- Gray, green, and brown lithic siltstone, shale, and sandstone. Copper sulfides and native copper occur locally near base

Lithology: siltstone; shale; sandstone

Porcupine Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Porcupine Volcanics - Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks

Lithology: basalt; andesite; rhyolite; medium-grained mixed clastic

Oronto Group; Nonesuch Shale (Middle Proterozoic) at surface, covers < 0.1 % of this area

Oronto Group; Nonesuch Shale - Gray, green, and brown lithic siltstone, shale, and sandstone. Copper sulfides and native copper occur locally near base

Lithology: siltstone; shale; sandstone

Menominee Group; Ironwood Iron-formation (Early Proterozoic) at surface, covers 0.6 % of this area

Menominee Group; Ironwood Iron-formation- Interbedded cherty and slaty iron-formation. Locally, secondary enrichment has formed "soft ore" bodies. In eastern part of Gogebic Range, Ironwood Iron-formation is intercalated with pyroclastic rocks of Emperor Volcanic Complex, and in eastern half of T. 47 N., R. 43 W. (where mapped within unit Xip) consists entirely of black slate

Lithology: iron formation; slate